Composition for passivating vanadium in catalytic cracking and preparation thereof

ABSTRACT

Disclosed is a vanadium trap for use in FCC which comprises a major amount of calcined kaolin clay, free magnesium oxide and an in situ formed magnesium silicate cement binder. Also disclosed are procedures for the preparation of the trap by forming a slurry in water of hydrous kaolin clay, magnesium oxide or magnesium hydroxide and sodium silicate, aging the slurry to form magnesium silicate in situ, optionally adding additional kaolin, colloidal silica or both, spray drying, and calcining the resulting spray dried microspheres without forming appreciable amounts of crystalline magnesium silicates or crystalline magnesium aluminates.

BACKGROUND OF THE INVENTION

This invention relates to magnesium oxide based compositions in the formof attrition-resistant fluidizable microspheres which are circulatedwith microspheres of zeolitic fluidizable cracking catalysts. Themagnesium oxide based particles minimize or prevent poisoning anddeactivation of the zeolitic cracking catalysts by vanadium contained inoil feedstock used in the catalytic cracking process. The inventionrelates also to processes for producing such compositions by spraydrying a slurry containing magnesium oxide, kaolin clay and in situformed inorganic cement.

Poisoning and deactivation of catalyst in FCC (fluid catalytic cracking)by vanadium in the oil feedstock is one of the most prominent problemsfaced by operators of oil refineries. Patents including disclosure ofthe use of alkaline earth compounds, including magnesium oxide, tomitigate the effects of vanadium include U.S. Pat. Nos. 4,465,779,4,549,548, 4,944,865, WO 82/00105, GB 218314A, EP-A-020151 andEP-A-0189267. In some of these references, the magnesium oxide iscontained in discrete particles, separate from the particles of zeolitecracking catalyst. EP-A-270,211 discloses discrete particles in whichmagnesium is present as a crystalline magnesium silicate, preferablyfosterite. The material containing crystalline magnesium silicate may beproduced by spray during a slurry containing magnesium carbonate andkaolin clay, followed by high temperature calcination to react themagnesium with silica in the clay, forming the crystalline magnesiumsilicate. Other disclosures of crystalline magnesium containingsilicates (clays such as sepiolite) appear in U.S. Pat. No. 4,549,548supra.

Efforts to develop products and processing modifications to mitigatevanadium passivation are by no means limited to the use of alkalineearth material. To the best of our knowledge, however, no magnesiumbased additive has enjoyed widespread commercial success. Certainperovskites such as barium titanate are employed commercially.Perovskites are expensive. Perovskites are not considered to be veryeffective in reducing SOx emissions in regenerator flue gas. Alkalineearth material, especially magnesium oxide, offers the additionalbenefit of reducing Sox in regenerator flue gas from cracking units.See, for example, WO 82/00105GB (supra).

There is strong motivation to utilize the inherent vanadium binding andSox capturing capacity of magnesium oxide in FCC operations utilizingfeedstocks having a high content of vanadium. References cited abovegive some indication of past efforts to produce magnesium oxide basedvanadium passivating particles adapted for co-circulating with zeolitecracking catalysts. Commercial success has not measured up to themotivation. One primary challenge was to provide a metals passivator ina physical form of particles sufficiently attrition-resistant for use inFCC, while maintaining the magnesium in most reactive form (oxide). Thisproblem was addressed in EP-A-270,211. The solution proposed in thatpatent application resulted in particles that were attrition-resistantin fresh form but lost hardness when subjected to steaming in testing.

Magnesium oxide without a binder/matrix is unsuitable for use in an FCCunit when it must be circulated through the reactor and regenerator ofan FCC unit along with cracking catalyst particles. This is becauseparticles of magnesium oxide readily break down into a powder whensubjected to attritive forces. Note that in one of the earliestproposals to use magnesia in an FCC unit to combat SOx (U.S. Pat. No.3,699,037), the material was circulated in the regenerator to bind SOx.The magnesia attrited during such use, eventually to be withdrawn fromthe regenerator with flue gas without circulating in the cracker, aswould be required to achieve vanadium passivation. Because of thefriable nature of magnesium oxide particles, the material did notcirculate with the catalyst during the FCC cycle.

Numerous patents, including several of those cited above, discloseformulations based on composites of magnesia with kaolin clay. Kaolinclay is a widely used matrix component for cracking catalyst because itis inexpensive and has potential binding properties. Also, it isrelatively catalytically inert in calcined form and is a prime candidateas a matrix/diluent for a vanadium passivator based on magnesia, whereincatalytic activity is not desired. An advantage of using kaolin clay asa matrix/diluent is that it can readily be formed into substantiallycatalytically inert particles by forming a dispersed concentrated fluidslurry to form microspheres, followed by spray drying. When dried,especially when calcined, kaolin also serves as a binding function.

Several of the references noted above provide examples of MgO/kaolinmicrospheres prepared by means including spray drying, but they do notdisclose the composition of the feed slurry to the spray dryer. They donot provide information about attrition-resistance. There is noindication that the inventors were concerned with attrition-resistanceor steam stability of the products. In the case of WO 82/00105GH, thematrix was a mixture of kaolin and silica-alumina gel, a conventionalmatrix for zeolite crystals in an active cracking catalyst.Silica-alumina is a material known to possess catalytic activity.

EP-A-270211, supra, refers to difficulties encountered in achievingattrition-resistance by mixing magnesia with kaolin clay, spray dryingand calcination.

Those skilled in the art of handling clays are aware that introductionof magnesium ions into clay slurries causes the slurry to flocculate andthicken. This has been used with benefit in the formulation of variousclay-based drilling mud. However, flocculation and thickening causesformidable problems in producing magnesia/kaolin clay products usefulfor FCC wherein particles of appreciable magnesium oxide content areproduced in spray dryers. It is a simple matter to provide a dispersedkaolin slurry that is sufficiently fluid at a high enough concentration(e.g., 50% solids) to produce coherent microspheres. However, if kaolinis spray dried at low solids, e.g., 10%, the microspheres will fallapart before they can be hardened by calcination. If magnesium is addedto such a high solids fluid dispersed slurry of kaolin in more than atrace amount, the slurry will flocculate and thicken. If enoughmagnesium ions are introduced, a solid gel forms and the slurry cannotbe formed into microspheres by spray drying using known technology.Addition of magnesium oxide to a kaolin slurry in amount sufficient toproduce spray dried particles having a sufficiently high MgO content foreffective vanadium passivation will result in a slurry that cannot bespray dried in continuous commercial spray drying equipment. Thisproblem plagued the inventors of the subject patent application in theirpursuit of developing attrition-resistance spray dried microspherescontaining magnesia with a clay diluent which meet the criteria for agood vanadium trap: attrition-resistance; high capacity for vanadiumtrapping; good vanadium passivation; and very high trapping efficiency(i.e., fast vanadium uptake).

To produce such particles it was necessary to overcome the difficultycaused by flocculation of a dispersed slurry of kaolin clay by theincorporation magnesium ions, resulting in thickening or even gelationof the slurry and, ultimately, the inability to formulate a slurry ofsufficiently high solids content to produce attrition-resistant spraydried microspheres. The need to control flocculation and thickening toachieve hardness was counterbalanced by the need to product microspheresthat were sufficiently porous to function as an effective magnesiumpassivator.

SUMMARY OF THE INVENTION

Novel vanadium passivation particles of the present invention are in theform of spray dried attrition-resistant microspheres composed of a minoramount of magnesium oxide, a major amount of calcined kaolin clayadmixed therewith and a small amount, relative to the magnesium ofoxide, of an in situ formed amorphous magnesium silicate cement. Theparticles have a low surface area and have minimal cracking activity.

Vanadium traps of the invention can be used with commercially availablezeolitic catalysts in FCC units where vanadium levels are high, therebyavoiding rapid catalyst deactivation. These traps permit refiners tooperate at lower catalyst make-up rates and will also reduce coke andgas associated with catalytic dehydrogenation by vanadium. The vanadiumcapacity of traps of the present invention is very high; the sulfatetolerance is excellent, is evidenced by the fact that essentially nosulfur remains on equilibrium vanadium traps of this invention. In thenear future, many more refiners will be using residual feeds which willincrease the vanadium concentration on the catalyst. The necessity touse efficient vanadium traps will therefore increase. Frequentlyfeedstock with a high vanadium concentration also contain high levels ofsulfur. The SOx binding capability of products of the invention is anadded benefit.

Products of this invention are obtained by processing steps comprisingmixing magnesium oxide or magnesium hydroxide, hydrous (uncalcined)kaolin clay and sodium silicate with water to form a dispersed fluidslurry which is aged. During aging, the basic magnesium compound reactswith sodium silicate to produce magnesium silicate which functions as abinder in the finished product. Optionally colloidal silica, additionalkaolin clay or both are added to the aged slurry. The proportion ofmagnesium oxide relative to sodium silicate is controlled to assure thatonly a small amount of magnesium silicate is formed, leaving the bulk ofthe magnesium oxide unreacted and available in the product to passivatemetals and, if desired, to bind SOx. The slurry is spray dried to formmicrospheres which are calcined under conditions sufficiently mild todehydrate the kaolin while preventing or minimizing the formation ofcrystalline magnesium silicate and/or magnesium aluminates.

One key manufacturing parameter which the inventors believe is crucialis the avoidance of large amounts of magnesium silicate formation insuch a way that only marginal reaction between the two components cantake place. Another key parameter is a moderate calcination temperaturewhich avoids the formation of significant amounts of crystallinemagnesium silicate and aluminate, thereby preserving the bulk of the MgOthroughout the process. A significant amount of crystalline magnesiumsilicate or aluminate would be a quantity such that more than about halfof the magnesium oxide is consumed in forming that crystalline material.Still another key parameter is assuring that the magnesium oxide is welldispersed from the time it is mixed with other ingredients to form aslurry until spray drying takes place. Thus, in order to produce thesemicrospheres in a form sufficiently attrition-resistant for use in FCCinvolves careful selection of starting materials (MgO, clay and binder)and making a careful selection of slurry preparation procedures prior tospray drying.

In one presently preferred embodiment of the invention, the vanadiumpassivator particles are obtained by spray drying a concentrated (highsolids) slurry of dispersed kaolin clay, dispersed magnesium oxide ormagnesium hydroxide, or mixtures thereof, sodium silicate, and,optionally colloidal silica, wherein the kaolin clay is introduced instages. In the initial stage, only a portion of the total kaolin clayincluded in the spray dryer feed slurry is mixed with magnesium oxide orhydroxide to form a low solids slurry, e.g., 30% solids. This slurry ispermitted to age and consumes only a small amount of the added magnesiumoxide or hydroxide. This results in the formation of a magnesiumsilicate cement by reaction of a small portion of the magnesia contentof the slurry with silica introduced as sodium silicate. Solids aresufficiently low in this slurry so that it is fluid in spite of the factthat it contains both kaolin clay and magnesium oxide. The remainingkaolin is injected into the first stage slurry using high shear staticmixing (as by an inline mixer) to form a fluid high solids slurry (e.g.,at least 50% solids). This slurry is immediately spray dried. The spraydried microspheres are then calcined at a time and temperaturesufficient to dehydrate the kaolin and harden the particles. It is notnecessary to wash the particles to remove solubles. Calcinationconditions are controlled to minimize the formation of crystallinemagnesium silicates or other crystalline magnesium compounds such asmagnesium aluminates. Some mullite may be present in an x-raydiffraction pattern of the product. Calcination converts the hydrouskaolin to the metakaolin state.

In another preferred embodiment, all of the kaolin is added to theslurry containing magnesium oxide. This slurry is aged to form somemagnesium silicate. Colloidal silica is preferably added and theresulting slurry is spray dried to form microspheres which are carefullycalcined.

DESCRIPTION OF PREFERRED EMBODIMENT

Typical properties of the spray-dried and calcined vanadium trapmicrospheres of the invention are as follows:

    ______________________________________                                                                     ESPECIALLY                                                 BROAD  PREFERRED   PREFERRED                                                  RANGE  RANGE       RANGE                                            ______________________________________                                        Bulk MgO.sup.(1), wt %                                                                    2-40     5-25        7-20                                         Free MgO.sup.(2), wt %                                                                    3-35     4-20        5-15                                         BET surface area,                                                                         0.1-25   1-20        2-15                                         m.sup.2 /g                                                                    Pore volume cc/g                                                                          0.1-0.4  0.15-0.35   0.15-0.30                                    EAI (attrition                                                                            0.1-2.0  0.2-1.5     0.3-1.3                                      resistance), wt %                                                             Roller attrition,                                                                         2-40     4-30        5-20                                         wt %                                                                          Average particle                                                                          50-120   55-100      55-90                                        size, microns                                                                 Average particles                                                                         5-50     7-40        10-35                                        <0-40 microns                                                                 ______________________________________                                         .sup.(1) By chemical analysis                                                 .sup.(2) By xray                                                         

Magnesium oxide in the crystalline form of periclass has been used inpractice of the invention. Another form of magnesium oxide that may beused is brucite. It is necessary to use a reactive form of magnesiumoxide but the reactivity will be selected with regard to the specificprocessing conditions employed, as explained hereinafter.

One procedure for making products of the invention on a laboratory scaleinvolves making down a slurry of hydrous kaolin (75 to 85 wt %, VFbasis), MgO (7-15 w t%, VF) , sodium silicate solution (preferablyhaving a Na₂ O/SiO₂ mole ratio of 0.35), and water on a high shear mixersuch as a Cowles mixer to form a fluid slurry having a total solidscontent of 25-35% by weight, expressed on a VF solid weight basis. Afterthe initial blending, this mixture is allowed to mix from 6 to 12 hoursin a slowly rotating container. During this "aging" step, magnesiumoxide reacts with sodium silicate and silica in the slurry to formmagnesium silicate which ultimately serves as a binder in the calcinedmicrospheres. Only a portion of the magnesium oxide reacts, whereby freemagnesium oxide (detectable by X-ray diffraction) is present in theproduct. The pH of the slurry increases during the reaction betweenmagnesium and silica. Aging may be carried out at ambient temperatureand pressure. After aging, colloidal silica (which serves as aco-binder) is added to the slurry (1-5 wt % VF SO₂) with enough water tomaintain a Brookfield viscosity of <1000 centipoises. The slurry is thenspray dried, preferably immediately to avoid thickening and gelation.Spray drying converts the slurry into microspheres with an averageparticle size equivalent to FCC catalyst (for example, average particlesize of about 75 microns) . These microspheres are then calcined incovered silica trays for 2 hrs. at 1800° F. Calcination "sets" thebinder(s), converts the hydrous kaolin to metakaolin and leaves freemagnesia in the microspheres.

This procedure has been employed using water-washed, high purity Georgiahydrous kaolin with particle sizes ranging from 60 to 90% by weightfiner than 2 microns, preferably from 75 to 80% finer than 2 microns. Inthis procedure, improved attrition due to finer clay particles and theuse of colloidal silica is off-set by a corresponding decrease inmacropore volume.

The MgO used in this procedure has a surf ace area (BET, nitrogen) from1 to 25 m² /g, with a median particle size from 1-10 microns. Preferredspecifications are 1 to 10 m² /g surface area and a median particle sizeof from 4 to 5 microns. When carrying out this processing, highersurface area MgO reacts too quickly in the clay slurry, producing softmicrospheres upon spray drying. Reduced amounts of MgO improve attritionbut also reduce the effectiveness of the MgO for vanadium passivation.The preferred amount is about 15 wt % in the finished product. Magnesiumshould not be used in the form of magnesium hydroxide or magnesiumcarbonate. Both give rise to problems due to particle shrinkage,ultimately resulting in vanadium traps having poor attrition resistance.

Sodium silicate binder as NO Brand (27% SiO₂, 9% Na₂ O=0.32 Na₂ O/SiO₂)increases particle attrition properties at higher levels but alsosignificantly reduces macroporosity. The preferred level is 1.25% asSiO₂ when using N Brand sodium silicate. Increased sodium silicatelevels increased attrition resistance of the particles up to a point.Higher levels of sodium silicate, however, undesirably reducedmacroporosity. Colloidal silica levels of from 1 to 5 wt %, preferably1.25 to 3.75% as SiO₂ are preferred. After addition of colloidal silicato the clay/MgO/sodium silicate slurry, the resulting colloidal silicaenriched slurry should be immediately spray dried to prevent thixotropicgelation.

The primary processing variable affecting hardness in this (as well asother variants of processes of the invention) is aging. The term agingrefers to the stage of processing wherein magnesium oxide on hydroxidereacts with sodium silicate in the clay/MgO/sodium silicate slurry.Excessive aging due to either undesirably high MgO reactivity (10 m² /gsurface area preferred), or excessively high initial slurry solids (<30%solid preferred) results in relatively soft particles.

The slurry may be spray dried in a conventional spray dryer (wheel ornozzle) and calcined. Typical spray dryer conditions are inlettemperatures of 650°-820° F. and outlet temperatures of 190°-230° F.Typical bed temperature during calcination is about 1800° F. Calcinationconditions used are sufficient to dehydrate the kaolin but insufficientto cause the characteristic kaolin exotherm to take place.

In another procedure, which is especially amenable to continuouscommercial implementation, addition of kaolin clay is staged to controlthe viscosity of the feed throughout processing and the grade ofmagnesia is selected to assure controlled aging. In this procedure,aging of the clay/Mgo slurry is controlled by making the initial MgOslurry using only a portion of the hydrous kaolin clay of the totalkaolin, e.g., 5-20% to be present in the feed charged to the spraydryer. Preferably ultrafine kaolin, e.g., 90-100% by weight finer than 2microns is used. A preferred level of hydrous clay is about 15% of thetotal hydrous kaolin. A lignosulfate dispersant should be used tomaintain the MgO in dispersed condition when using this procedure. Inpreparing the first, relatively low solids slurry, it is preferable tocofeed lignosulfonate dispersant and clay and then incorporate magnesiumoxide. This slurry is then aged, resulting in formation of magnesiumsilicate. The pH increases during aging and the viscosity of the slurryincreases. The remainder of the clay, preferably an ultrafine grade, isadded immediately before spray drying so as to assure minimal contacttime between the additional clay and the initial slurry. The remainderof the clay is preferably added as a concentrated fluid dispersion,e.g., a slurry containing 68-70% solids, to assure that the spray dryeroperates with a high enough solids slurry to assure anattrition-resistant product. These microspheres are formed by spraydrying, as described above, and are then calcined in covered trays for 2hrs. at 1800° F. in laboratory scale operations. Using commercial rotarycalciners a bed temperature of about 1800° F. is suitable.

For this two stage kaolin clay addition procedure, a more reactive(light burned) MgO is desired with a surface area of from about 5 to 70m² /g. The preferred surface area is 35 to 65 m² /g. High surface areaMgO is suitable in this procedure because of the minimized contact timewith the bulk of the clay slurry prior to spray drying.

Using this two stage kaolin addition procedure, a sodium silicate binderprecursor with a molar ratio of SiO₂ /Na₂ O of 2.88 has proved betterthan sodium silicates with a 3.12-3.25 molar ratio. Levels of thepreferred sodium silicate are from 0.75 to 2.5 wt % as SiO₂. A preferredlevel is of about 2% SiO₂. [All weights of SiO₂ referred to are reportedon a VF weight basis.)

The addition of colloidal silica in this two stage kaolin additionprocedure is optional. The benefit of enhanced attrition achievable byadding colloidal silica (which is made to the first slurry for thisprocedure) is weighed against the increase in the solids and increase inviscosity of the initial MgO/kaolin clay slurry. Lower solids preventpremature aging of the slurry and softer particles.

Passivator microspheres of the invention are used to prevent vanadiumpoisoning of zeolitic cracking catalyst used to crack gas oil andresids. The active catalyst particles contain one or more zeolites,usually including at least one of the Y type, in a matrix/diluent,typically silica-alumina. The catalysts may be prepared by in situprocedures, e.g., processes described in U.S. Pat. No. 4,493,902, or byprocedures in which previously crystallized zeolite is mixed with matrixcomponents, e.g., kaolin and silica-alumina gel. Generally particles ofzeolitic cracking catalyst and passivator are similar in size, althoughthey can be different if desired.

Passivator microspheres of the invention may be blended with separatezeolite catalyst particles before introducing the catalyst to an FCCunit. Alternatively, the passivator particles can be charged tocirculatory catalyst inventory in the cracking unit. Typically theparticles are mixed in amounts within the range of 2 to 50% by weight,preferably 10 to 40% by weight, and most preferably 20 to 30% by weightof the mixture. When used in insufficient amounts, improvements invanadium passivation may not be sufficient. When employed in excessiveamounts, cracking activity and/or selectivity may be impaired. Optimumproportions vary with vanadium level of feed and the proportion ofmagnesia in the passivator particles.

In the specification and illustrative examples, the following proceduresfor measuring and characterizing materials were used.

All proportions are on a weight basis.

The term "VF" weight refers to volatile free weight and is determined byheating a sample to constant weight at 1800° F.

Surface area measurements were by the known BET method using nitrogen asadsorbate.

The particle sizes of clay materials used in preparing samples weredetermined by conventional sedimentation procedure.

Attrition resistance is reported by EAI and Roller attrition values. TheRoller Procedure is described in U.S. Pat. No. 5,082,814, the teachingsof which regarding this test procedure are incorporated herein bycross-reference. The EAI procedures is described in U.S. Pat. No.4,493,902, incorporated herein by cross-reference.

Catalytic activity was measured by the MAT procedure described in U.S.Pat. No. 4,493,902, the teachings of which are incorporated herein bycross-reference. Porosity measurements are made by mercury porosimetryas set forth in this patent.

Percent "free" MgO was determined by conventional X-ray diffraction bymeasuring and adding the integrated peak intensity of the three MgO XRDlines at 42.9°, 62.3° and 78.6° 2θ, using Cu K-alpha radiation andcomparing the values to those of a pure MgO standard.

In all of the illustrative examples, MgO was in periclase form.

The following procedure was used in some of the illustrative examples todeposit vanadium prior to catalytic evaluation. This procedure isbelieved to give more realistic results than the known Mitchell methodbecause it takes into account transfer of vanadium from zeoliticcracking catalyst particles to vanadium trap particles during the FCCcycle. In this method, a neutral body (kaolin clay particles calcined at2150° F. for 2 hours) was first impregnated with vanadium. The surfacearea of these particles was less than 3 m² /g; the particles had noactivity for catalytic cracking. Vanadium migration from these particlesto blended FCC catalyst particles was measured after steaming at 1450°F. for 4 hours in a 90% steam/10% air atmosphere. In a blend containing70% of a regular FCC catalyst (sample B described below) with mesh sizeof 230-325 (US Standard) and V impregnated on neutral particles (A),only 5% of the V was retained by sample A. This indicates the V would bereleased from sample A to the FCC catalyst (sample B) during steamingwhich would mimic the FCC operation more accurately than the Mitchellimpregnation method.

To prepare sample A, vanadium containing particles, vanadium fromvanadium naphthenates was deposited over a chemically neutralmicrospheres by using vanadium naphthenates of 1.5% concentration inhexane over 500 grams of a highly calcined clay (2100° F.) to obtain aloading of about 1500 ppm vanadium. The impregnated particles were thendried overnight and calcined first at 700° F. and then 11000F. vanadiumanalysis of these particles showed the presence of 7500 ppm. Vanadiumwas analyzed by inductively coupled plasma spectroscopy (ICP).

To prepare sample B, a commercial FCC catalyst manufactured by EngelhardCorporation was used. The catalyst contained (40%) Y-zeolite and wasexchanged to a rare-earth oxide level of 0.8%.

Neutral particles with no V sink were highly calcined kaolin clayparticles (2150° F.) that had less than 3 m² /g surface area and nilcatalytic cracking activity.

Vanadium trap microspheres are described in illustrative examples.

In carrying out the new procedure, 15 grams of the FCC catalyst (sampleB) were blended with 20% (by weight) of sample C and 30% of sample A sothat the finished catalyst contained 50% FCC catalyst with a vanadiumlevel of 2500 ppm. The blended material was then steamed in 90%steam/10% air at 1450OF for 4 hours in a closed reactor. The catalystblend was then analyzed before and after steaming to confirm that thecomposition of the blend did not change during steaming.

EXAMPLE #1 Procedure for Testing Unreacted Magnesium oxide

Tests were carried out to determine parameters for preserving magnesiumoxide while forming a binder of magnesium oxide in situ. The componentsused were as follows:

    ______________________________________                                        Hydrous Clay        814 g                                                     MgO AM94            140.7 g                                                   N ® Brand Sodium Silicate                                                                     37.9 g                                                    H.sub.2 O           1298.7 g                                                  Colloid Silica (added)                                                                            248.0 g                                                   ______________________________________                                    

A slurry consisting of a hydrous (ASP®-600 supplied by EngelhardCorporation) , Mgo (American Mineral's AM 94, surface area of 10 m² /g),N®Brand sodium silicate and water were made down using a high sheardrill press mixer. This mixture was then allowed to age over night in aslowly rotating container. After aging, a colloidal silica solution(Nalco #2326) was added to the mixture with enough water to maintain aflowable mixture (<1000 CPS Brookfield viscosity, #2 spindle). Thisslurry was then screened to remove any agglomerates, and spray dried toa particle size similar to FCC catalyst (˜70u APS) . Calcination of thespray dried microspheres was performed at temperatures of from1500°-1900° F. @2 hrs. The following table indicates that as thecalcination temperature is increased, pore volume decreases, attritionimproves and the formation of periclase (as measured by XRD) isdecreased.

    ______________________________________                                        Calcination Temp.                                                                        PV          Free MgO  Roller                                       °F. (600-20K)   %         Attrition, %                                 ______________________________________                                        1500       0.3346      12.5      >30                                          1800       0.2115      10.8      17                                           1900       0.1047       8.3      10                                           2100       --           7.0      --                                           ______________________________________                                    

EXAMPLE 190 2 Preparation and Testing of Control Microspheres

A slurry consisting of a hydrous clay (ASP®600 supplied by EngelhardCorporation), tetrasodium pyrophosphate clay dispersant (10 lb/ton) andwater were made down to a clay solids content of 60% by weight using ahigh shear drill press mixer. This grade of kaolin is approximately 80%by weight finer than 2 microns. The slurry was screened to remove anyagglomerates, and spray dried to a particle size similar to FCC catalyst(˜70u APS). The spray dried particles were then calcined at 2150° F. for2 hours and designated sample C. The kinetic activity of sample C wasless than <0.1.

Kinetic activity is calculated as follows: ##EQU1## wherein conversionis on a weight basis

The effectiveness of these particles as a vanadium trap was tested bythe new procedure described above. Fifteen (15) grams of FCC catalystwas blended with 6 grams of sample C and 9 grams of sample A, wherebythe final catalyst contained 2500 ppm V. After steaming in 90% steam/10%air for 4 hours at 1450620 F., the sample was tested for catalyticactivity by the MAT procedure: The kinetic activity of the steamedcatalyst was 1.0.

This procedure was used f or comparing blends in which the inertparticles C were substituted by samples which contained M90 as avanadium trap.

EXAMPLE #3

This example further demonstrates the importance of providing freemagnesium oxide in clay-based vanadium passivator particles. In thisexample, the magnesium oxide starting material was converted tocrystalline magnesium compounds as a result of the use of excessivelyhigh temperature during final calcination.

Hydrous kaolin clay microspheres made according to Example 2 werecalcined at 1300° F. for 1 hour to transform the clay to the metakaolinform. 100 grams of the metakaolin microspheres was impregnated with 100grams of magnesium nitrate solution containing 10% Mgo. The microsphereswere dried at 250° F. and calcined at 2100° F. in a muffle furnace for 2hours. These microspheres were designated sample G.

The surface area of the calcined microspheres was less than 1 m² /g; XRDanalysis showed the presence primarily of mullite, fosterite,(crystalline magnesium silicate) cristobalite, anatase, rutile andspinel (MgAlO₃) No free MgO was observed in these microspheres.

These microspheres, tested as a V trap, had an activity of only 1.1which is only 10% better than the control.

EXAMPLE #4

In this example, magnesium carbonate was used as the source ofmagnesium. Colloidal silica was used as a binder. Calcination was atrelatively high temperature (2100° F.).

A slurry consisting of a hydrous kaolin clay (ASP®600 supplied byEngelhard Corporation) , MgO (Premier's 33 MGCO₃), N®Brand sodiumsilicate and water was made down using a high shear drill press mixer.This mixture was then allowed to age overnight in a slowly rotatingcontainer. After aging, colloidal silica (Nalco #2326) was added to themixture with enough water to maintain a flowable mixture (<1000 CPSBrookfield viscosity) . This slurry was then screened to remove anyagglomerates, and spray dried to a particle size similar to FCC catalyst(˜70u APS).

Specific amounts of reagents were as follows:

    ______________________________________                                        Hydrous clay        814.0 g                                                   MgCO.sub.3 (50% slurry)                                                                           630.0 g                                                   N ® Brand sodium silicate                                                                     43.9 g                                                    Water               550.0 g                                                   Colloidal Silica solution                                                                         254.4 g                                                   (15% SiO.sub.2 by Wt)                                                         ______________________________________                                    

Spray drying conditions were as follows:

    ______________________________________                                        Inlet Temp           600-650° C.                                       Outlet Temp          240-260° C.                                       Air Pressure          40 psig                                                 Pump Rate             1                                                       ______________________________________                                    

The dried microspheres were then calcined at a temperature of 2100° F.@2 hrs. These microspheres were designated sample H.

    ______________________________________                                                Surface     Pore Volume Roller                                        Sample  Area, m2/g  600-20KA, cc/g                                                                            Attrition, %                                  ______________________________________                                        H        2.2        0.25        >30                                           I       13.5        0.38          6                                           ______________________________________                                    

Sample H was tested for vanadium control. Activity was 1.2 which is 20%better than the control, sample C.

EXAMPLE #5

This example further demonstrates the desirability of maintainingappreciable free Mgo in a vanadium trap.

A portion of the spray dried microspheres of Example 4 were calcined at1800° F. This material was sample I. An X-ray diffraction pattern of thecalcined microspheres showed high level of free MgO, which the inventorsconsider a necessary component for an effective vanadium trap. Thesemicrospheres tested in the same manner as described in Example #1,showed an activity of 1.5, about 50% higher activity than the control.

EXAMPLE 190 6

This example illustrates an embodiment of the process of the inventioncarried out in plant-scale equipment.

Processing of the spray dryer slurry consisted of initially mixing NBrand sodium silicate, water, carboxyl methyl cellulose (used as asuspending agent for magnesium oxide) and a slurry of hydrous kaolinclay in a high shear mixer. The kaolin clay was nominally 80% by weightfiner than 2 microns. This was followed by the addition of AmericanMineral's AM 94 MgO (surface area of 50 m² /g) to achieve 12% MgO in theproduct. Prior to spray drying, Nalco colloidal silica (15% silica) wasadded to the slurry using an inline mixer. The solids content of theslurry was 33% by weight prior to addition of the colloidal silica and31% after addition of the silica. The material was spray dried to aparticle size slightly coarser than an FCC catalyst, averaging about 80microns.

Component ratios were as follows:

    ______________________________________                                                            wt.                                                       ______________________________________                                        Hydrous Clay Slurry   100                                                     N Brand sodium silicate solution                                                                    2.07                                                    MgO                   7.86                                                    H.sub.2 O             76.87                                                   CMC                   6.16                                                    Colloidal Silica      15.39                                                   ______________________________________                                    

The spray dried microspheres were calcined in a commercial rotarycalciner at a furnace temperature of about 2100° F. (which correspondsto a laboratory calcination at 1700° to 1800° F. These calcinedmicrospheres were designated sample J and were tested as in Example 1.They exhibited about 35% higher activity than particles C with novanadium trap.

EXAMPLE #7

This example further shows the necessity for controlling calcinationtemperature to maintain free magnesium oxide in the passivatorparticles.

Processing was the same as in Example #6 except with a high calcinationtemperature of 2300° F. was used in operating the rotary calciner. Thiscorresponds to a laboratory calcination temperature of from 2000-2200°F. The material calcined at 2300° F. was designated sample K.

Testing of sample K indicated similar activity maintenance to sample Cand 35% lower than Example #6, sample J.

The Mitchell procedure for testing vanadium tolerance was used in thefollowing example. Twenty-eight (28) grams of an FCC catalyst containingabout 35% zeolite and 1.2% rare-earth oxide was blended with 12 grams ofeither neutral microspheres (no vanadium trap, sample C) or with samplescontaining MgO as a V trap. The blended particles were then impregnatedwith a solution of Ni and V naphthenates in cyclohexane solution. Theimpregnated material was then dried in air overnight and then calcinedin a muf f 1e furnace at 700° F. for 2 hours followed by calcination at1100° F. for another 2 hours. Two levels of naphthenate solutions wereimpregnated over the blended particle to give finished productscontaining (1) Ni/V of 1000/2000 ppm and (2) 2500/5000 ppm. The sampleswere then steamed in a 90% steam/10% air for 4 hours at 1450° F. Thesamples were analyzed before and after steaming to demonstrate thatsimilar compositions were maintained during steaming. Microactivitytesting was then performed.

EXAMPLE #8

This example shows the calcination temperature sensitivity as testedunder the Mitchell method protocol.

Twenty-eight (28) grams of commercial FCC catalyst from EngelhardCorporation containing about 35% zeolite and a rare-earth oxide level of1.2% was blended with 12 grams of either of the following components:inert kaolin particles (C), highly calcined MgO/clay particles K (fromExample 7), or low-temperature calcined MgO/clay particles i (fromExample 6). The three mixtures were then impregnated with metals, usingthe Mitchell method.

At metals levels of 2000 ppm V/1000 ppm Ni, the mixture containingparticles K had the same activity maintenance as the reference sample;the mixture containing particles of J] had 23% better activitymaintenance. At 8000 ppm V/2500 ppm Ni, the activity maintenanceimprovements over sample C were 20% for the mixture containing particlesK, and 50% for the mixture containing particles J.

The results clearly show that the lower level of calcination whichretains high level of unreacted Mgo in the particles had betterperformance than the control, sample C.

EXAMPLE #9

This example illustrates a presently preferred method for practicing theinvention.

For this process, the spray dryer feed slurry was prepared as twoseparate components which were combined in a static mixer immediatelyprior to spray drying. The first component "A" is composed of anultrafine particle size Georgia Yaolin (10o% finer than 1 micron) madeinto a 59.34% VF slurry with water and tetrasodium pyrophosphate (TSPP)as a dispersant. These high solids were achieved by blending a 44.7%solids clay slurry with sufficient spray dried kaolin and optimum TSPPin a high shear cowles mixer.

The second component "B" consisted of M90, as supplied by MartinMarietta Corporation as MagChem 40, #14 Grade sodium silicate providedby Power Silicates (41% solids, 2.88 molar SO₂ :Na₂ O Ratio) , HP-100, adispersant supplied by Martin Marietta and believed to be alignosulfonate, the same ultrafine particle size clay used in component"A" supplied as a 44.7% VF solids slurry and sufficient water to a totalVF solids of this component of 27.87%.

Component "B" was produced in a series of high shear Cowles mixers. Inthe first mixer, all the components except the MgO were added in theproportions listed below; in the second, the dry MgO was introduced andits addition rate was controlled by solids measurement.

    ______________________________________                                               MIXER #1                                                               ______________________________________                                               Clay Slurry                                                                            23.49%                                                               #14 Silicate                                                                           7.97%                                                                HP-100   .10%                                                                 H.sub.2 O                                                                              68.44%                                                        ______________________________________                                    

Target=14.04% VF solids and 2.55% SiO₂ from #14 silicate

    ______________________________________                                        MIXER #2                                                                      ______________________________________                                        Mixer #1 Slurry  83.91%                                                       MgO              19.18%                                                       ______________________________________                                    

Target=27.87% VF solids

Component "B" slurry was then allowed to age in an agitated tank for aminimum of 6 hrs. prior to spray drying. Sufficient agitation wasrequired to maintain the viscosity of this component at ˜1000centipoises by Brookfield measurement.

For spray drying, component "A" (the high solids clay slurry) andcomponent "B" (the aged Mgo slurry) were combined in a static mixer inthe ratio of 1.337:1 respectively, and immediately pumped directly tothe spray dryer atomizer. Target VF solids of the spray dryer slurry was45.9%. Component ratios of the microsphere on a VF weight bases are: 15%MgO, 2.0% SiO₂ (provided from #14 silicate binder), 0.29% HP-100.

The spray dryer inlet temperature was regulated to maintain an outlettemperature of from 200°-205° F. and the atomizer speed used to controlparticle size distribution of the spray dried microspheres. Calcinationon a direct fired rotary calciner followed spray drying with inlettemperatures of from 2000°-2200° F. to meet targeted finished productparameters.

We claim:
 1. A spray drying process for manufacturing microspheresuseful in fluid cracking of vanadium containing oil feedstock withseparate fluidable microspheres containing a zeolitic crackingcomponent, said process comprising mixing kaolin clay, magnesium oxideor magnesium hydroxide, and sodium silicate with water to form a slurry,aging said slurry to react a portion of the magnesium oxide or hydroxidewith silica to form a magnesium silicate, spray drying the aged slurryto form microspheres comprising magnesium oxide, kaolin clay and in situformed magnesium silicate, and calcining said microspheres for a timeand temperature sufficient to dehydrate the kaolin clay but insufficientto form a significant amount of crystalline magnesium silicates oraluminates.
 2. The process of claim 1 wherein colloidal silica, kaolinclay or a combination thereof is added to the aged slurry before spraydrying.
 3. The process of claim 1 wherein a portion of the kaolin clayin the slurry that is sprayed dried is added before again and additionalkaolin clay is added to the aged slurry in an inline mixer.
 4. A spraydrying process for manufacturing attrition-resistant fluidizablemicrospheres comprising magnesium oxide in a kaolin clay matrix, saidparticles being useful in fluid cracking of oil feedstock with aseparate fluidable microspheres containing a zeolitic cracking componentto passivate vanadium originally contained in oil feedstock whichcomprises: forming a first fluid dispersed slurry (A) comprising water,kaolin clay, sodium silicate and magnesium oxide and a dispersant formagnesium oxide; aging said slurry; adding additional kaolin clay tosaid aged slurry to form a second slurry (B) having higher solidscontent than slurry (A) using high shear agitation sufficient tomaintain said slurry fluid in spite of its higher content of solids;immediately spray drying said slurry B while it is still fluid;recovering the resulting microspheres comprising free magnesium oxideand kaolin clay; and calcining the microspheres for a time andtemperature sufficient to dehydrate the kaolin but insufficient to causethe kaolin to undergo the characteristic kaolin exotherm or to formcrystalline magnesium silicates or aluminates.
 5. The process of claim 1wherein the calcined microspheres contain from 2 to 40% by weight Mgo.6. The process of claim 1 wherein the calcined microspheres contain from5 to 25% by weight MgO.
 7. The process of claim 1 wherein the calcinedmicrospheres contain from 7 to 20% by weight MgO.
 8. The process ofclaim 4 wherein said slurry A and said slurry B have an apparentviscosity below 1000 cp when measured by a Brookfield viscometer using a#2 spindle.
 9. The process of claim 4 wherein said additional kaolin isadded to said slurry B by an inline mixer which provides the high shearagitation.
 10. The process of claim 4 wherein all of the kaolin clay isabout 100% by weight finer than 1 microns.
 11. The process of claim 4wherein said sodium silicate has a mole ratio of SiO₂ /Na₂ O of about2.88.
 12. Attrition-resistant microspheres useful as a vanadium trap influid catalytic cracking, said microspheres comprising particles of freeMgO in amount of at least 2% by weight, determined by X-ray, inadmixture with particles of fine particle size anhydrous, X-rayamorphous kaolin clay, and a small amount of a magnesium silicatecement, the anhydrous kaolin being the predominating component of saidmicrospheres, said microspheres having a BET surf ace area below 15 m²/g, being free from substantial amounts of crystalline magnesiumsilicate and crystalline magnesium aluminate phases, and having an EAIbelow 2% by weight before and after steaming at 1480° F. for 4 hourswith 100% steam, and a total pore volume in the range of 0.1 to 0.4cc/g.
 13. The microspheres of claim 12 wherein the free MgO content isfrom 5-25% by weight.
 14. The microspheres of claim 12 wherein the freeMgO content is from 7-20% by weight.
 15. The microspheres of claim 12,which have a total pore volume in the range of 0.15 to 0.35 cc/g. 16.The microspheres of claim 12 which have a total pore volume in the rangeof 0.15 to 0.3 cc/g.
 17. The microspheres of claim 12 which have asurface area below 10 m² /g.